1. Field of the Invention
The present invention relates to an inverter for LCD backlight, and in particular, to an inverter for LCD backlight that is capable of operating an analog dimming control, a PWM dimming control or a complex dimming control by means of a control signal set by a manufacturer, and in case of the complex dimming control, realizing an original circuit operated by a controlling method distinguished from the conventional controlling method to enhance responsive characteristics when shifting a dimming mode.
2. Description of the Prior Art
In general, an inverter refers to a converting device for converting a direct current to an alternating current. Devices commonly used for an inverter are a combination of a direct current motor with an alternating current power generator, a vibrator or a discharge tube, or a transistor or a thyristor.
Such an inverter is a general power supply exclusively used for a mobile alternating power supply, a fluorescent power supply for a vehicle, an emergency power supply in case of interruption, or a backlight power supply for LCD or other display devices.
The currently available dimming methods of a controller for a backlight inverter are roughly classified into an analog dimming and a PWM dimming that have different circuit structures according to their operations.
Depending on the characteristics of an object to be controlled, any one of the analog dimming method or the PWM dimming method has been used. However, each method has some drawbacks of being unstable.
A complex dimming has been suggested in recent days so that either the analog dimming method or the PWM dimming method can be used, if necessary, by applying both methods. The complex dimming is performed by selectively using all the circuits according to each dimming method.
However, the conventional method described above has a problem of overlap in its construction due to an equipment of both an analog dimming circuit and a PWM dimming circuit, thereby enlarging the volume and complicating a layout in addition to the difficulties in maintenance and repair. Moreover, conversion from the analog dimming to the PWM dimming causes a problem of deteriorating the responsive characteristics.
It is, therefore, an object of the present invention to provide an inverter for LCD backlight that can eliminate an overlap in a circuit construction and operate with an analog dimming or a PWM dimming by a control signal set by a manufacturer, or can control with a complex dimming to realize an independent circuit in a controlling manner distinguished from the conventional controlling manner to enhance responsive characteristics when converting a dimming mode in a complex dimming control.
To achieve the above object, there is provided an inverter for LCD backlight, comprising: a first switching element connected to an input terminal of a DC/AC converter, which operates a lamp by using an input power, for supplying an input power; a dimming control section for comparing a first dimming signal with a second dimming signal inputted from outside in accordance with a dimming mode selection signal, outputting a first control signal, a second control signal and a third control signal to control a PWM dimming, an analog dimming or a complex dimming control; an error amplifier for receiving a feedback signal F/B of a feedback part connected to the lamp by means of an inverting terminal, and receiving the first control signal outputted from the dimming control signal by means of a non-inverting terminal to output a compared signal in accordance with a state of a signal inputted to each terminal; a first comparator for receiving a third control signal outputted from a pyramidal wave for controlling the PWM dimming having a predetermined cycle or the third control signal outputted from the dimming control section by means of the non-inverting terminal, receiving the second control signal outputted from the dimming control section by means of the non-inverting terminal so as to be compared with the third control signal and output a signal based on the resultant value; a second switching element connected between an output terminal of the error amplifier and a ground terminal for performing on/off operations in accordance with a voltage level of a signal outputted from the first comparator, and converting a potential of the output terminal of the error amplifier to a ground potential during the xe2x80x9conxe2x80x9d operation; and a second comparator for receiving the output signal from the error amplifier by means of the non-inverting terminal, receiving an oscillating signal of a predetermined cycle through the non-inverting terminal so as to be compared with the output signal from the error amplifier, and control on/off operations of the first switching element in accordance with the resultant value.
In the inverter for LCD backlight according to the present invention, the dimming control section comprises: comparing means for comparing the first dimming signal with a reference signal, outputting the compared signal to consider a state of the second dimming signal connected to the output terminal or a state of an output signal by feeding back the output signal thereof; second control signal generating means for controlling a state of the second control signal by reference to the signal loaded at the output terminal of the comparing means so as to be applied to an input terminal of inverting data of the first comparator; mode selecting means for controlling a state of the third control signal by means of the mode selection signal, and adjusting a state of the first control signal; and first control signal generating means for generating a signal to distinguish an analog dimming from a PWM dimming by means of the mode selection signal outputted from the mode selecting means, and generating a first control signal so as to be applied to a non-inverting data input terminal of the error amplifier.
In the inverter for LCD backlight according to one aspect of the present invention, when the dimming control section operates in the analog dimming mode by means of he mode selection signal, the third control signal has a ground potential by means of the mode selecting means, and the first control signal and the second control signal output lineally escalating signals so that the second comparator in charge of on/off of the first switching element can be controlled by the output signal of the error amplifier.
In the inverter for LCD backlight according to another aspect of the present invention, when the dimming control section operates in the PWM dimming mode by means of the mode selection signal, the third control signal has a potential of a high level by means of the mode selecting means, and the first control signal has a potential of a high level by means of the first control signal generating means, while the second control signal outputs lineally escalating signals by means of the second control signal generating means so that the second comparator in charge of on/off of the first switching element can be controlled by the second switching means operated on/off under a control by the first comparator.
In the inverter for LCD backlight according to another aspect of the present invention, when the dimming control section operates in a complex dimming control mode by means of the mode selecting signal, the third control signal has a potential of a high level by means of the mode selecting means, and the second control signal outputs lineally escalating signals by means of the second control signal generating means, while the first control signal lineally elevates in a ground potential state at a predetermined point of time by means of the first control signal generating means so that the first control signal operates in a PWM dimming control mode under a ground potential state, and that the first control signal operates in an analog dimming control mode in a lineally escalating interval.